Changeset 200807 in webkit

Timestamp:

May 12, 2016 6:55:40 PM (8 years ago)

Author:

mmaxfield@apple.com

Message:

Source/WebCore:
[Cocoa] Text shadow sometimes clipped unexpectedly
​https://bugs.webkit.org/show_bug.cgi?id=108929

Reviewed by Dean Jackson.

CoreGraphics can only draw one text shadow at a time. We work around that by drawing
the text multiple times, one for each shadow. However, we want to make sure that the
original text isn't also drawn multiple times, so we bump up the shadow offsets so
the text and the shadow don't intersect, and then we clip out the original text (so
only the shadow remains).

Unfortunately, this clipping requires knowing where the visual extent of the text is,
which WebKit currently has trouble with. In particular, we often use layout extents
in lieu of visual extents, which is a problem when the glyphs draw outside of their
layout boxes. In this case, it causes us to think the text shadow is much smaller
than it really is, so our clipping operation clips to an area which is too small.

A quick solution to this is to inflate the clip rect by an amount proportional to the
font size, and offset the text shadow accordingly. If this amount is large enough,
this bug will occur on few enough sites that it is reasonable to consider this bug
fixed without the real solution of educating WebKit properly about the difference
between text layout rects and text visual extent rects.

Test: fast/text/multiple-text-shadow-overflow-layout-rect.html

• rendering/TextPainter.cpp:

(WebCore::ShadowApplier::ShadowApplier):

LayoutTests:
Text shadow sometimes clipped unexpectedly
​https://bugs.webkit.org/show_bug.cgi?id=108929

Reviewed by Dean Jackson.

Add a font which draws dramatically far outside of its layout rect.

• fast/text/multiple-text-shadow-overflow-layout-rect-expected.html: Added.
• fast/text/multiple-text-shadow-overflow-layout-rect.html: Added.
• fast/text/resources/font-overflow-layout-rect.svg: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/fast/text/multiple-text-shadow-overflow-layout-rect-expected.html (added)
• LayoutTests/fast/text/multiple-text-shadow-overflow-layout-rect.html (added)
• LayoutTests/fast/text/resources/font-overflow-layout-rect.svg (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/TextPainter.cpp (modified) (2 diffs)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2016-05-12  Myles C. Maxfield  <mmaxfield@apple.com>
+
+        Text shadow sometimes clipped unexpectedly
+        https://bugs.webkit.org/show_bug.cgi?id=108929
+
+        Reviewed by Dean Jackson.
+
+        Add a font which draws dramatically far outside of its layout rect.
+
+        * fast/text/multiple-text-shadow-overflow-layout-rect-expected.html: Added.
+        * fast/text/multiple-text-shadow-overflow-layout-rect.html: Added.
+        * fast/text/resources/font-overflow-layout-rect.svg: Added.
+
 2016-05-12  Ryan Haddad  <ryanhaddad@apple.com>
 

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2016-05-12  Myles C. Maxfield  <mmaxfield@apple.com>
+
+        [Cocoa] Text shadow sometimes clipped unexpectedly
+        https://bugs.webkit.org/show_bug.cgi?id=108929
+
+        Reviewed by Dean Jackson.
+
+        CoreGraphics can only draw one text shadow at a time. We work around that by drawing
+        the text multiple times, one for each shadow. However, we want to make sure that the
+        original text isn't also drawn multiple times, so we bump up the shadow offsets so
+        the text and the shadow don't intersect, and then we clip out the original text (so
+        only the shadow remains).
+
+        Unfortunately, this clipping requires knowing where the visual extent of the text is,
+        which WebKit currently has trouble with. In particular, we often use layout extents
+        in lieu of visual extents, which is a problem when the glyphs draw outside of their
+        layout boxes. In this case, it causes us to think the text shadow is much smaller
+        than it really is, so our clipping operation clips to an area which is too small.
+
+        A quick solution to this is to inflate the clip rect by an amount proportional to the
+        font size, and offset the text shadow accordingly. If this amount is large enough,
+        this bug will occur on few enough sites that it is reasonable to consider this bug
+        fixed without the real solution of educating WebKit properly about the difference
+        between text layout rects and text visual extent rects.
+
+        Test: fast/text/multiple-text-shadow-overflow-layout-rect.html
+
+        * rendering/TextPainter.cpp:
+        (WebCore::ShadowApplier::ShadowApplier):
+
 2016-05-12  Myles C. Maxfield  <mmaxfield@apple.com>
 

trunk/Source/WebCore/rendering/TextPainter.cpp

@@ -55 +55 @@
     if (m_onlyDrawsShadow) {
         FloatRect shadowRect(textRect);
-        shadowRect.inflate(shadow->paintingExtent());
+        shadowRect.inflate(shadow->paintingExtent() + 3 * textRect.height());
         shadowRect.move(shadowOffset);
         context.save();
@@ -61 +61 @@
 
         m_didSaveContext = true;
-        m_extraOffset = FloatSize(0, 2 * textRect.height() + std::max(0.0f, shadowOffset.height()) + shadowRadius);
+        m_extraOffset = FloatSize(0, 2 * shadowRect.height() + std::max(0.0f, shadowOffset.height()) + shadowRadius);
         shadowOffset -= m_extraOffset;
     }